Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $166.98   11.561%   $186.2846   $186.28   $186.30   $186.30  
  Purchase #2 $164.87   10.764%   $182.6166   $182.62   $182.60   $182.60  
  Purchase #3 $146.38   13.256%   $165.7841   $165.78   $165.80   $165.80  
  Purchase #4 $132.60   9.735%   $145.5086   $145.51   $145.50   $145.50  
  Purchase #5 $9.80   13.491%   $11.1221   $11.12   $11.10   $11.10  
  Purchase #6 $245.75   11.460%   $273.913   $273.91   $273.90   $273.90  
  Purchase #7 $200.33   4.328%   $209.0003   $209.00   $209.00   $209.00  
  7 purchase totals = $1,066.71       $1,174.2293   $1,174.22   $1,174.20   $1,174.20